In a typical inkjet recording or printing system ink droplets are ejected from a nozzle at high speed towards a recording element or medium to produce an image on the medium. The ink droplets, or recording liquid, generally comprise a recording agent such as a dye or pigment and a large amount of solvent. The solvent or carrier liquid typically is made up of an aqueous mixture, for example, comprising water and one or more organic materials, such as a monohydric alcohol, a polyhydric alcohol or the like.
An inkjet receiver or recording element typically comprises a support having on at least one surface thereof at least one ink-receiving layer. There are generally two types of ink-receiving layers. The first type of ink-receiving layer comprises a non-porous coating of a polymer with a high capacity for swelling, the non-porous coating absorbing ink by molecular diffusion. Cationic or anionic substances may be added to the coating to serve as a dye-fixing agent or mordant for a cationic or anionic dye. Typically, the support is a smooth resin-coated paper and the coating is optically transparent and very smooth, leading to a very high gloss “photograde” inkjet recording element. The swellable binder forms a barrier to air-borne pollutants that may degrade the image dye over time. However, this type of ink-receiving layer usually tends to absorb the ink slowly and consequently the imaged receiver or print is not instantaneously dry to the touch.
The second type of ink-receiving layer comprises a porous coating of inorganic, polymeric or organic-inorganic composite particles, a polymeric binder and optional additives, such as dye-fixing agents or mordants. These particles can vary in chemical composition, size, shape, and intra-particle porosity. In this case, the printing liquid is absorbed into the open interconnected pores of the ink-receiving layers substantially by capillary action to obtain a print that is instantaneously dry to the touch. Typically the total interconnected inter-particle pore volume of porous media, which may include one or more layers, is more than sufficient to hold all the applied ink forming the image. Image dyes adsorbed to the porous particles are exposed to air and may fade unacceptably in a short time.
Bringley et al., in WO-A-2005/009747, describe porous inkjet media containing core/shell particles wherein the shell of the particles is an oligomeric or polymeric aluminosilicate complex or aluminosilicate particulate and the preferred core materials are those with a negative surface charge, such as silica. The resistance to fading of image dyes printed on the medium is improved compared with standard particles of silica or alumina. Such particles exhibit a relatively high density, so considerable weight is required for an ink-receptive layer.
Wexler, in U.S. Pat. No. 6,475,603, discloses an inkjet recording element comprising a porous uppermost layer containing core-shell particles, wherein the core is a thermoplastic polymer and the shell comprises a shell of inorganic colloidal particles, preferably colloidal alumina or colloidal silica. Preferred polymeric core materials include polyester, acrylic polymer and polystyrene. The receiver is intended for fusing after printing to form a film sealing the material. Improved gloss and reduction of cracking were observed. Improvement in dye stabilization properties was not reported.
Kaeding, et al., in U.S. Pat. No. 6,726,991, disclose core/shell particles comprising a core of porous polymer and a shell of inorganic colloid having a median diameter of less than about 70 nm. The inorganic colloid particles are selected from silica, alumina, alumina-silica and the like. The preparation method provides small particle size, narrow size distribution without organic emulsifiers. Crosslinking monomers provide particle porosity for applications such as controlled release of pharmaceutical agents. Improvement in dye stabilization properties of inkjet receivers was not reported.